1. Field of the Invention
The present invention relates to a digital television broadcasting receiving apparatus capable of receiving a digital television broadcasting signal, a control method for the digital television receiving apparatus, and a control program for the digital television receiving apparatus.
2. Related Background Art
Generally, in digital television broadcasting, video and audio data signals (MPEG signals) of a plurality of channels, compressed by the Moving Picture Experts Group (MPEG) standards, and digital data are multiplexed to broadcast multiplexed digital television signals. A digital television broadcasting receiving apparatus receives multiplexed digital television broadcasting signals with an antenna or the like, demodulates the signals by a predetermined modulation method such as Quadrature Phase Shift Keying (QPSK) and Quadrature Amplitude Modulation (16QAM), separates the multiplexed Signals into video and audio data and digital data of a desired program, performs a decoding process (decodes) the video and audio data compressed by the MPEG standards, and outputs the decoded signals via a video output circuit and an audio output circuit to a monitor and a speaker (refer to Japanese Patent Application No. H09-298752).
Video data compressed by the MPEG standards is constituted of three types of compressed frames: an I picture, a P picture and a B picture (refer to FIG. 2). The I picture is data capable of being decoded by itself, whereas the P and B pictures are difference data requiring reference frames. Namely, the P and B pictures can be decoded into video data, by using the P and B pictures on the basis of the I picture. However, since decoding starts from the I picture, if a channel is to be changed over between the program being viewed and another program, decoding the video data of the changed program starts after the I picture appears. Namely, an image to be displayed cannot be generated until the I picture appears, so that a monitor of the digital television broadcasting receiving apparatus for displaying an image displays no image.
The digital television broadcasting receiving apparatus of the type described above is structured to effect signal processing and operation processing in accordance with an operation program stored in a memory (if the receiver has a hardware circuit for effecting signal processing and operation processing, this circuit effects signal processing and operation processing). The BS digital broadcasting operation rules defined by the corporation, Association of Radio Industries and Businesses (alias: ARIB) describe that in BS digital broadcasting “Software of a receiver is corrected. Bug fixing, correction of defects caused by a difference of operation interpretations between a transmitter and a receiver, improvements on display, improvements on response speed, usage operation, and etc are performed.” In order to satisfy the rules, update program data is sent being contained in digital television broadcasting signals, the update program data solving defects of, and improving the function of, an operation program of a digital television broadcasting receiving apparatus. Transmission of the update program data is not limited to a BS digital broadcasting.
Namely, the above-described digital data contains not only contents data and the like to be used by digital television broadcasting but also program data (so-called update program data) for a digital television broadcasting receiving apparatus in operation. When a broadcasting station transmits the digital broadcasting signals containing update program data for a digital television broadcasting receiving apparatus to the digital television broadcasting receiving apparatus, the broadcasting station transmits the update program data by utilizing an idle time between transmission of the video and audio data. A digital television broadcasting receiving apparatus is structured in the following manner. If the update program data is contained in the digital television broadcasting signals, the digital television broadcasting receiving apparatus checks whether a vendor name (maker name) and a receiver model are compatible with those of the digital television broadcasting receiving apparatus. If this check indicates that the vendor name and receiver model are compatible, the digital television broadcasting receiving apparatus stores (downloads) the update program data in a predetermined program data storage area of, e.g., a non-volatile memory.
If the update program is stored, an update process is performed to update the program stored previously to the newly stored update program. However, for this update process, the operation program used previously is required to be stopped (namely, decoding is required to be stopped). Since images to be displayed cannot be generated during this period, the update process for the program is generally performed when a restart is performed (when a power is turned on next). Therefore, particularly in the case in which a power of a digital television broadcasting receiving apparatus is not turned off for a long period, the operation program is not updated immediately, even if the new update program for eliminating defects and improving the function has already been acquired. There arises therefore a problem that it is not possible to eliminate defects and improve the function, until a restart is performed (until a power is turned on next).
Generally, the digital television broadcasting receiving apparatus of the type described above has a memory for storing the operation program and various data. In order to effectively use the memory capacity, a process is executed to retain memory blocks having a necessary capacity only when necessary, and to release the memory blocks when unnecessary. However, if memory blocks are repetitively retained and released, memory blocks still not used are finely divided and become fragmentary. If the memory continues to be used in this state, the operation program and various data are dispersed in the memory. There is a fear that an access speed lowers and the function of the digital television broadcasting receiving apparatus is degraded. It is therefore necessary to relocate memory blocks not in use and memory blocks in use, and to collect memory blocks in use so as not to disperse the operation program and various data to be stored next. However, the digital television broadcasting receiving apparatus of this type requires a large amount of calculation processing ability (so-called CPU power) of decoding MPEG signals and the like. Therefore, if the calculation processing ability (CPU power) is assigned to memory relocation, then there arises a fear that images to be displayed cannot be generated because MPEG signals cannot be decoded (i.e., because there is a necessity of stopping decoding). In order to suppress generation of such defects, memory relocation has been performed when a restart is performed (when the power is turned on next).